This invention relates to a device for detecting current flowing in an electric wire, and more particularly to a device of this kind which detects current flowing in an electric wire in an indirect manner by detecting the intensity of a magnetic field produced by the current.
Conventional current detecting devices include a type generally employed in ordinary type ammeters, which detects current in a direct manner by causing current to flow through a fixed resistance, and detecting a voltage drop between input and output terminals of the fixed resistance as representing the current. Another conventional type detects current in an indirect manner such that a magnetic core is arranged around an electric wire in which current flows, a magnetic field produced by the current is collected by the magnetic core, and the intensity of the magnetic field is detected in terms of voltage by means of a magnetic-to-electric transducer such as a Hall element and a magnetic reluctance element.
According to the former type, due to the direct detection of the current by means of the fixed resistance, there are disadvantages that electric power is consumed by the resistance, resulting in large power loss, the maximum current that can be detected is limited as the maximum allowable current that can flow through the fixed resistance is limited, the resistance value of the fixed resistance can vary due to heat generated in the fixed resistance by current flowing therein, resulting in an error in the detected current value. On the other hand, according to the latter type, although it is free of the above-mentioned disadvantages with the former type, if it is applied to detecting current flowing in one of a plurality of electric wires extending parallel with each other, it cannot accurately detect the current flowing in the one electric wire since the intensity of magnetic fields formed around the other electric wires is undesirably also detected by the magnetic-to-electric transducer provided in the magnetic core.